Electrical submersible pumps (ESP) are widely used to pump oil production wells. A typical ESP has a rotary pump driven by an electrical motor. A seal section is located between the pump and the motor to reduce the differential between the well fluid pressure on the exterior of the motor and the lubricant pressure within the motor. A drive shaft, normally in several sections, extends from the motor through the seal section and into the pump for rotating the pump. The pump may be a centrifugal pump having a large number of stages, each stage having an impeller and diffuser.
A typical ESP motor has a motor housing that surrounds a lamination stack, or stator, which in turn defines a stator bore. The stator bore contains a plurality of stacked rotor sections, each mounted on a motor shaft for rotating the shaft. The motor housing and stator lamination stack are stationary, and the rotor sections and motor shaft rotate relative thereto. An annular gap is located between the rotor sections and the stator lamination stack. Normally, the motor, including the gap, is filled with a dielectric motor lubricant.
Typically, the ESP motor is oriented vertically in a well bore. Accordingly, the rotor sections require lateral support within the stator bore. Generally, this lateral support is provided by radial bearings. The bearings are separate from and positioned between the rotor sections. Each bearing includes an outer bushing that contacts the inner edges of the stator laminations to prevent rotation of the outer bushing relative to the stator laminations. Each bearing has an inner sleeve that rotates with the shaft and is in sliding engagement with the outer bushing.
While these motor bearings work well, they add to the component cost to the motor. Also, additional time is required to install the bearings while assembling the motor.